Yes, there are quite a few out there. You can start by looking on popular fanfic websites like Archive of Our Own. Just search for 'luffy x lucy heartfilia' and you'll find a variety of stories with different plotlines and writing styles.
One common theme is adventure. Since Luffy is an adventurer in One Piece and Lucy has her own adventures in Fairy Tail, it's natural for their fanfics to involve them going on exciting quests together.
A great plot twist could be that one of the Fairy Tail guys, like Loke, is actually a double agent working for an enemy guild. Lucy discovers this and has to decide whether to trust him again or turn him in. It would create a lot of internal conflict for her.
A third theme is self - discovery. Her anger makes her re - evaluate who she is and what she's capable of. This can lead to her exploring different aspects of her magic, her relationships, and her place in the guild or the magical world at large. It's a way for the authors to show Lucy growing and evolving as a character.
Another fanfic could focus on Lucy's relationship with Erza. Maybe they team up for a tournament within the Fairy Tail guild. Along the way, they face tough opponents and have to rely on each other's strengths. Lucy's strategic thinking combined with Erza's powerful combat skills would make for an exciting story.
Another theme is the exploration of magic. Lucy has her celestial magic, and the OC usually has some form of unique magic as well. The fanfictions often explore how their different magics can work together or clash. It's interesting to see how the authors play with the magic system in the Fairy Tail universe to create new and exciting storylines for Lucy and the OC.
First, you need to know both universes well. Research Naruto's abilities, his friends, and the world of ninja. Do the same for Lucy Heartfilia in the 'Fairy Tail' world. Then, think of an interesting plot. It could be a simple adventure where they meet by chance and have to work together. Or a more complex story about saving both their worlds from a great threat. Next, focus on character development. How would they interact? How would they change each other? And don't forget to write in a way that shows your passion for both characters.
You can start by looking on fanfiction.net. It has a large collection of Fairy Tail fanfictions, including those with an OC and Lucy Heartfilia. Just use the search function and type in relevant keywords.
One great story could be 'The OC's Adventure with Lucy'. In it, the original character has a unique magic that complements Lucy's celestial magic. They go on a quest to find a lost celestial key, facing various challenges along the way. It's full of action and the developing relationship between the OC and Lucy is really interesting.
Well, obviously she'll interact with her past self. It would be really interesting to see how she reacts to seeing a younger and more naive version of herself. She could also meet characters who are no longer alive in the present. For example, if there were any great wizards from the past who played important roles in the history of magic. Additionally, she might cross paths with some of the villains from the past who were causing trouble long before the current villains in the story. This could change her perspective on the whole conflict in the present.